Patent GB-1169139-A (GB)
Title: Drive and Coupling apparatus for a Control Element of a Nuclear Reactor
IPC: G21C7/12
Filed: 1968-10-08
Abstract: 1,169,139. Controlling reactors. COMBUSTION ENG., Inc. 8 Oct., 1968 [10 Oct., 1967], No. 47681/68. Heading G6C. The control rod 74 of a nuclear reactor is connectable to an extension shaft 122 mounted coaxially within a sleeve 106, rack teeth 108 on the surface of which are drivingly engaged by a pinion coupled to a drive shaft disposed in parallel offset relation to the sleeve 106. The cruciform control rod head 76 is received within slot openings 86 in the lower portion 84 of a cylindrical coupling tube 80, the upper portion of which has a splined socket 82. Within the coupling tube 80, a reciprocal locking plunger 92 is operable to releasably engage the top of the control rod head 76. The plunger 92 is biased upwardly by a spring 94 which engages the underside of the plunger head 96 and a stop 98 integral with the coupling tube 80. The lower end of the rack sleeve 106 is provided with a splined head 114 which engages in the splined socket 82. The upper end of the sleeve 106 has a head 118 which cooperates with the inner surface of a guide cylinder 116. The extension shaft 122 is integral at its lower end to the upper end of the locking plunger 92 and extends upwardly through and beyond the sleeve 106 where screw threads 128 are provided to receive a releasable connector 124. This connector 124 is screwed down on to the head 118 so as to securely fasten the shaft 122 to the sleeve 106. The upper end of the shaft 122 is in the form of an elongated stem 130 having grooves 132 to receive detent balls 134 carried by the connector 124 for locking it to the shaft 122. The balls 134 are housed in apertures in a cylindrical member 144 atop the nut body 136 of the connector 124 and are forced into and out of the grooves 132 by means of a detent operator 154 through an opening 162 in the top of which an operating tool may be inserted. The detent operator 154 is biased into its locking position by means of a spring 168 extending between the top of the nut body 136 and the bottom of the operator 154. Disengagement of the control rods 74 from their associated drive mechanisms such that the closure head can be removed from the reactor vessel is effected using a tool 172 (Fig. 7) comprising an outer sleeve 174 with a reduced diameter portion 180 at its lower end sized to be inserted through the opening 162 in the detent operator 154 and provided with circumferentially spaced ribs 182 which engage in slots 166 in the operator 154 and thus enable it to be rotated. Detent balls 184 located at the lower end of the portion 180 co-operate with an annular relief groove 186 in the cylindrical member 144 to lock the tool to the connector 124. These detents are operated by a plunger 188 biased into the looking position by means of a spring 190. The reactor is shut down with all the control rods 74 in their fully extended positions (their lower ends approximately 2" above the bottom of the core) and the tool 172 inserted with the plunger 188 retracted into the bore 162 of a detent operator 154. The plunger 188 is then released and the tool secured to the connector 124. At the same time, the detent operator 154 is pressed down against the spring 168 so as to cause the balls 134 to be retracted from their locking engagement in the grooves 132 on the stem 130, thereby permitting the connector 124 to be rotated, first to lower the control rod 74 until it rests on the core bottom and then to remove the connector 124 from the shaft 122. The tool is then withdrawn and the drive motor operated to retract the sleeve 106 from the splined socket 82 to thus completely sever the connection between the drive mechanism and the control rods. This process is repeated for each of the drive mechanisms after which the closure head can be removed.